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We report recent progress on work concerning challenges in ion-beam solid investigations[1]:
- dynamics of plasma decay
- development of sub-nanosecond pulsed ion beams
- threshold behaviour of heavy ions.
Coincidence measurements between backscattered and secondary electrons were performed on an Al (100) crystal in order to study the correlation between plasmon decay and secondary electron emission. A large contribution of surface excitations to the peak of secondaries could be directly observed in this way. Furthermore, the influence of the secondary electron cascade was found to be unexpectedly weak. This measurement was performed on a classical coincidence system with two hemispherical analyzers which only allows such studies on materials with pronounced plasmon loss peaks.
Therefore, we are presently building a magnetic field time-of-flight spectrometer to conduct measurements of secondary electrons induced by ions or electrons. The system uses sub-ns ion or electron pulses giving full momentum information of emitted electrons at the time of emission. The magnetic field forces the emitted electrons on a cyclotron trajectory and all electrons which energy is below a certain limit will be projected on the MCP. Therefore, the transmission of MoVES is considerably higher compared to conventional electron spectrometers. Detection of up to 14 electrons per projectile impact allows to conduct coincidence measurements. Due to the high transmission the coincidence rate is significantly improved in comparison to a conventional coincidence spectroscopy system even for a laboratory system. Results of first measurements are presented.
- [1] RA. Baragiola, Invited review: Some challenging unsolved problems in atomic collisions in solids, Nucl. Instr. and Meth. in Phys. Res. B 237 (2005) 520.
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